Preparation of dialkyl disulfides



United States Patent 3,134,798 lPREPARATl-SN @F DEALKYL DTSULFHDES William L. Fierce and Roger L. Weichman, Crystal Lake,

and W alter 3i. Sandner, Carpentersville, 113., assignors to The Pure Gil Company, ialatine, 111., a corporation of Qhio No Drawing. Filed Aug. 2, 1961, Ser. No. 128,677

12 Claims. (Cl. 26t)-4S3) This invention relates to new and useful improvements in processes for the prep ration of dialkyl disulfides, and more particularly to the preparation of dialkyl disulfides by partial oxidation of primary and secondary mercaptans with nitrogen dioxide.

The chemistry of organic sulfur compounds has been investigated extensively in recent years as a result of the necessity for removing sulfur compounds from petroleum fractions. Mercaptans occur extensively in petroleum or are produced in the refining of petroleum fractions, and the utilization of these compounds is important if maximum return is to be obtained for petroleum products. Alkyl sulfides and disulfides are well-known organic sulfur compounds which have a variety of uses. These compounds are intermediate in the formation of other sulfur-containing organic compounds and in some cases are useful as solvents. Mercaptans have been oxidized to dialkyl disulfides by a variety of oxidizing agents, see Organic Chemistry of Bivalent Sulfur, Reid, Chemical Publishing Company, 1958. Mercaptans have been oxidized by air or oxygen in the presence of aqueous alkali. Mercaptans have also been oxidized by ozone, permanganates, perborates, fuming nitric acid, chlorine, iodine, etc. The various techniques of oxidation of mercaptans with the oxidation agents reported in the prior art give rise to a variety of products. In some cases monosulfides are formed, while in other cases disulfides or polysulfides are formed. In many cases the sulfides which are formed in the oxidation process are further oxidized to sulfones, sulfoxides, and sulfonic acids.

It is therefore one object of this invention to provide a new and improved process for the preparation of dialkyl disulfides and alkyl thionitrites in good yield and high selectivity.

A feature of this invention is the provision of an improved process for the preparation of dialkyl disulfides and alkyl thionitrites by reaction of nitrogen dioxide with a primary or secondary aliphatic mercaptan. Another feature of this invention is the provision of an improved process for the preparation of diallryl disulfides and alkyl thionitrites in which a primary or secondary C -C alkyl mercaptan is reacted with nitrogen dioxide at a temperature of about 50 to +250 C. under essentially anhydrous conditions.

Other objects and features of this invention will be come apparent from time to time throughout the specification and claims as hereinafter related.

This invention is based upon our discovery that dialkyl disulfides can be produced in excellent yields, together with small amounts of alkyl thionitrites, by the uncatalyzed reaction of primary or secondary alkyl mercaptans with nitrogen dioxide under essentially anhydrous conditions. The reaction is exothermic and takes place readily at room temperature although it may be carried out at ambient temperatures ranging from 50 to +250 C. In carrying out this process, a primary or secondary alkyl mercaptan (preferably a C C primary or secondary allcyl mercaptan) is contacted with nitrogen dioxide in a reactor. The reaction can be carried out in any convenient reaction system, and the reactor may be of any material of construction which is inert toward the reactants and products of reaction under reaction conditions. The reactor may be made of glass,

quartz, stainless steel, etc. When the mercaptan is mixed with nitrogen dioxide, an instantaneous exothermic reaction takes place which completely consumes the nitrogen dioxide (unless an excess of nitrogen dioxide is used). When a lower mercaptan (e.g., CH SH, C H SH, C H SH) is reacted, the reaction is preferably carried out in the gas phase. When a higher boiling mercaptan is reacted, the nitrogen dioxide is bubbled through (or otherwise contacted with) the liquid mercaptan. The raio of reactants in the gas-phase reaction is not critical and the mercaptan and nitrogen dioxide may be fed in widely varying mol ratios ranging from 1:10 to 20:1. When the reaction is carried out in liquid phase, it is preferred to avoid the use of a stoichiometric excess of nitrogen dioxide as the results in the formation of sulfoxides or sulfones rather than the desired disulfides. The rate of feed of reactants is not critical and the total gaseous hourly space velocity of reactants in the gasphase reaction may vary widely from as little as to as high as 5000 or more. Equivalent feed rates can be used in the liquid-phase reaction. The reaction products are withdrawn from the reaction zone, and settle into two phases. The lower phase consists essentially of water and some dissolved products. The upper phase, which is bright red, consists essentially of a dialkyl disulfide (derived from the mercaptan) containing in solution a small amount of an allcyl thionitrite. When the upper phase is separated, dried, and heated, the thionitrite is decomposed and a substantially pure dialkyl disulfide is obtained as the product. This process is limited to the reaction of nitrogen dioxide with primary and secondary alkyl mercaptans under essentially anhydrous conditions (i.e., free of water other than the byproduct water of reaction). Mercaptans which may be used in this reaction include methanethiol, ethanethiol, propanethiol (both primary and secondary isomers), pentanethiol, hexanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, etc.

The following non-limiting examples are illustrative of the scope of this invention.

EXAMPLE I A 21-mm. O.D. glass reactor-tube, having a volume of 92 cc., was mounted vertically and connected so that two separate gas streams could be charged at the top. Helium at cc./min. was bubbled through ethanethiol at room temperature and charged to the reactor tube at an ethanethiol flow rate of 46 cc./min. Nitrogen dioxide gas was also charged at the top of the reactor tube at a rate of 39 cc./min. At the point in the reactor tube where the two gas streams met, there was an exothermic reaction with the formation of a liquid product.

The gaseous and liquid products of the reaction were withdrawn from the bottom of the reactor over a coldfinger condenser and into a large glass receiver. From this point, gaseous products were directed through a condenser and then a gas-sampling tube. The final gaseous product was essentially colorless, thus indicating that most of the nitrogen dioxide had been consumed in the reaction. After a run of 45 minutes duration, there was obtained 6.6 ml. of a liquid product which had separated into two phases. The lower phase (0.7 ml.) was almost colorless while the upper phase (5.9 ml.) was cherry-red.

The lower liquid phase was separated and analyzed by infrared spectroscopy. This phase was found to consist essentially of water. The upper phase was analyzed by infrared spectroscopy and found to consist of about diethyl disulfide, together with a small amount of diethyl sulfide. The intense red color was an indication of the formation of ethyl thionitrite (there is no accurate method of analysis for thionitrites). Mass spectrometric analyses of the charge and product gas samples showed that nitric oxide was a major gaseous product while a minor amount of sulfur dioxide was formed.

In this run, ethanethiol and nitrogen dioxide were fed in a mol ratio of 1.18 mols of the former to 1 mol of the latter. In the reaction, 91.2% of the ethanethiol was consumed and diethyl disulfide Was formed in a yield of 73.4% (based on ethanethiol charged) and a selectivity of 80.5% (based on ethanethiol consumed in the reaction). In this reaction there was also produced a small amount of dimethyl disulfide which resulted from a small amount (6.5%) of methanethiol in the feed.

EXAMPLE II The apparatus described in Example I is used for carrying out the reaction of methanethiol with nitrogen dioxide. Helium diluent at 50 cc./min. and methane-thiol gas at 110 cc./min. are charged to the top of the reactor tube. Nitrogen dioxide gas at 50 cc./min. is also charged to the top of the reactor tube. At the point in the tube where the gas streams mix, there is an exothermic reaction with the formation of a liquid product. The liquid product is separated as in Example I and an aqueous phase is separated and discarded. The non-aqueous phase consists of a major amount of dimethyl disulfide and a minor amount of methyl thionitrite, together with small amounts of dimethyl sulfide. In this reaction, dimethyl disulfide can be produced in yields inexcess of 70% and selectivities approaching 100%.

EXAMPLE III An apparatus similar to that used in Example I is used for the reaction of various mercaptans with nitrogen di oxide under the conditions set forth in Table I and with the results indicated therein. The only change in procedure is that the mercaptans are charged to the reactor tube as liquids.

disulfide and unreacted ethanethiol were the major components. In this experiment about 54% of the mercaptan was consumed. Diethyl disulfide was obtained in a yield of about 30% based on the nitrogen dioxide charged to the reaction.

EXAMPLE V A gas flask, equipped with a stirrer and bubbler tube, was charged with 150 g. n-dodecanethiol (0.741 mol) and 200 ml. carbon tetrachloride. Gaseous nitrogen dioxide cc./min.) and nitrogen (20 cc./min.) were bubbled into the stirred liquid mixture until 6.7 g. (0.146 mol) nitrogen dioxide were charged. The temperature of the reaction mixture was maintained at 24 C. during the reaction. In this experiment di-dodecyl disulfide was obtained with the yield of 84.2% based on the nitrogen dioxide (limiting reactant) charged.

When the same reaction was carried out using water as the diluent for the reaction, the yield of the product disulfide was less than half obtained using a non-aqueous solvent.

From the foregoing examples and other experimental work, we have found that good yields of dialkyl disulfides and alkyl thionitrites can be obtained by the reaction of nitrogen dioxide with one or more primary or secondary alkanethiols at ambient temperatures. Where low-molecular-weight mercaptans are used as the reactant, the reaction is preferably carried out in gas phase,

' although a liquid-phase reaction in an inert solvent (such as carbon tetrachloride, hydrocarbons, etc.) can be used. The reaction is carried out at temperatures in the range of about to +250 C, at a mercaptan/nitrogen dioxide mol ratio in the range of about 1:10 to 20:1. The reaction is preferably carried out at temperatures of about 0-'30 C. In the gas-phase reaction, the reaction can be carried out using a wide range of reactant ratios. In the liquid-phase reaction an excess of nitrogen diox- T able I Mercaptan 053551; Products N O 2 0 Ratio GHQCHCHQ 2.5 CH3 CH3 CH3 SI-I (1HSSCH+('3HSNO 0 Ha C H: JHa

CHaCI-IzCH2CH2SH. 2. 5 n-C4H9-S-S11C H +I1C H9SNO CHaCHOHzCHzCHm..- 2.5 CH3 CH3 CH3 S H 3HSS(JH+ HSNO 33E111 Cali-I1 CHsHy n C H SI-I 2. 5 220 I1C5H7S-SI1CBII17+IICBH17SNO EXAMPLE IV A glass flask was charged with 32.7 g, liquid ethanethiol and a mixture of helium and nitrogen dioxide was bubbled therethrough at 30 cc./min. each for 110 minutes. The total amount of nitrogen dioxide charged provided a mercaptan/nitrogen dioxide mol ratio of 3.1:1. On contact with the nitrogen dioxide, the ethanethiol reddened and the color progressively deepened. The red color is attributed to the formation of ethyl thionitrite' (which is deep red in color), but no analytical procedure for identification of thionitrites is available. The gaseous effluent from the flask was colorless, thus indicating that no unreacted nitrogen dioxide was present. The final liquid product consisted of two phases, a deep cherry red upper phase and a small amount of a clear, colorless lower phase (mostly water). Analysis of the product gas by mass spectrometer showed that it contained helium, nitric oxide, ethanethiol, and water. Distillation and an infrared analysis of the red liquid showed that diethyl ide should be avoided since it tends to reduce the yield of disulfides by forming solid reaction products. In the liquid-phase reaction, the use of an inert solvent is preferred and the reaction should be carried out under substantially anhydrous conditions (i.e., in the absence of water other than the by-product water of reaction). The reaction is limited to primary and secondary mercaptans since the reactions of tertiary mercaptans with nitrogen dioxide usually produces alkyl thionitrates.

While we have described our invention fully and completely with special emphasis on several preferred embodiments thereof, We wish it to be understood that within the scope of the appended claims this invention may be practiced otherwise than as specifically described herein.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows:

1. A method of preparing dialkyl disulfides and alkyl thionitrites which comprises reacting nitrogen dioxide under anhydrous conditions with at least one alkyl mercaptan selected from the group consisting of primary and secondary mercaptans, at a mercaptan/nitrogen dioxide mol ratio in the range of about 1:10 to 2011 with the provision that a stoichiometric excess of said mercaptan is used when the reaction is carried out in liquid phase, and a reaction temperature of about -50 to +250 C.

2. A method in accordance with claim 1 in which the mercaptan reactant 1's methanethiol and the product is a mixture of dimethyl disulfide and methyl thionitrite.

3. A method in accordance with claim 1 in which the mercaptan reactant is ethanethiol and the product is a mixture of diethyl disulfide and ethyl thionitrite.

4. A method in accordance with claim 1 in which methanethiol and nitrogen dioxide are mixed at room temperature to effect a spontaneous exothermic reaction and a liquid product is obtained consisting essentially of a mixture of dimethyl disulfide and methyl thionitrite.

5. A method in accordance with claim 1 in which ethanethiol and nitrogen dioxide are mixed at room temperature to efiect a spontaneous exothermic reaction and a liquid product is obtained consisting essentially of a mixture of diethyl disulfide and ethyl thionitrite.

6. A method in accordance with claim 1 in which the reaction is carried out in an inert non-aqueous diluent.

7. A method in accordance with claim 6 in which nitrogen dioxide is bubbled into a mixture of n-dodecanethiol and carbon tetrachloride to produce di-n-dodecyl disulfide.

8. A method in accordance with claim 1 in which the reaction is carried out at a temperature of about 30 C.

9. A method for the partial oxidation of mercaptans whihc comprises reacting nitrogen dioxide under anhydrous conditions with at least one alkyl mercaptan selected from the group consisting of primary and secondary mercaptans, at a temperature of about to +250 C., said reaction being carried out in liquid phase using a stoichiometric excess of said mercaptan, and recovering an organic product containing a major portion of a dialkyl disulfide.

10. A method for the partial oxidation of mercaptans which comprises reacting nitrogen dixoxide under anhydrous conditions with at least one lower alkyl mercaptan selected from the group consisting of primary and secondary mercaptans, at a temperature of about 50 to +250 C., said reaction being carried out in gas phase at a total gaseous hourly space velocity of reactants in the range from about 50 to 5,000, and recovering an organic product containing a major portion of a dialkyl disulfide.

11. A method of preparing dialkyl disulfides and alkyl thionitrites which comprise reacting nitrogen dioxide under anhydrous conditions with at least one lower alkyl mercaptan selected from the group consisting of primary and secondary mercaptans, said reaction being carried out in gas phase at a mercaptan/nitrogen dioxide mol ratio in the range of about 1:10 to 20:1 and at a temperature of about 50 to +250 C.

12. A method in accordance with claim 11 in which the total gaseous hourly space velocity of reactants is in the range from about 50 to 5000.

References Cited in the file of this patent UNITED STATES PATENTS 1,908,935 Tschunkur et a1 May 16, 1933 2,307,624 George Jan. 5, 1943 2,328,709 Crandall et al Sept. 7, 1943 UNITED STATES PATENTEOFFICE CERTIFICATE OF CORRECTION Patent No, $134,798

William L. Fierce et a1,

s in the above numbered pattters Patentshould read as May 26 196 It is hereby certified that error appear d that the said Le ent reqliring correction an corrected below.

Column 2 line 10, for "raio" read ratio line 15 for "the first occurrence, read this column 5 line 33, for "whihc" read which column 6 line 9 for "dixoxide" read dioxide Signed and sealed this 27th day of October 1964,

(SEAL) Abtest:

EDWARD J. BRENNER ERNEST Wm SWIDER I Aitesting Ufficei' Commissioner of Patents UNITED STATES PATENTCFFICE CERTIFICATE OF CORRECTION Patent No. $134,798

William L. Fierce et a1 ears in the above numbered pat- I It is hereby certified that error app ent requiring correction and that the said Letters Patent should read as corrected below May 26 1964 line 10, for "raio" read ratio line l5 read this column 5 line column o line 9 for Column 2 for "the", first occurrence,

33. for "'whihc" read which "dixoxide" read dioxide sealed this 27th day of October 19640 Signed and (SEAL) Attest:

ERNEST W. SWIDER i EDWARD J. BRENNER Attesting Officer 7 Commissioner of Patents 

1. A METHOD OF PREPARING DIALKYL DISULFIDES AND ALKYL THIONITRITES WHICH COMPRISES REACTING NITROGEN DIOXIDE UNDER ANHYDROUS CONDITIONS WITH AT LEAST ONE ALKYL MERCAPTAN SELECTED FROM THE GROUP CONSISTING OF PRIMARY AND SECONDARY MERCAPTANS, AT A MERCAPTAN/NITROGEN DIOXIDE MOL RATIO IN THE RANGE OF ABOUT 1:10 TO 20:1 WITH THE PROVISION THAT A STOICHIOMETRIC EXCESS OF SAID MERCAPTAN IS USED WHEN THE REACTION IS CARRIED OUT IN LIQUID PHASE, AND A REACTION TEMPERATURE OF ABOUT -50* TO +250*C. 